Group A served as the control and did not receive any treatment, group B received 5mg/kg mercury chloride

only for three weeks, group C received 500mg/kg of ethanolic extract of Aloe barbadensis for 3 weeks, groups

D and E received 5mg/kg of mercury chloride for 3 weeks followed by 250mg/kg and 500mg/kg of ethanolic

extract of Aloe barbadensis for 3 weeks respectively. All administrations were via oral gavage. Anxiety index

and recognition memory were evaluated using open field and novel object recognition tests. Blood was obtained

via ocular puncture for serum estimation of superoxide dismutase (SOD), malondialdehyde (MDA) levels. Brain

tissue obtained were homogenized for estimation of Acetylcholinesterase (AChE) and glutamate levels and also

processed for routine Hematoxylin and eosin and silver Beilschowsky staining. Results of the neurobehavioural

tests showed significant (P<0.05) increase in anxiety indexwhen comparand significant decrease (P<0.05) in

recognition index in group B. There was significant (P<0.05) decrease in SOD, AChE, glutamatelevels in group

Keywords— Mercury chloride, oxidative stress, amyloid plaques, Alzheimer’s disease, Aloe barbadensis

INTRODUCTION

Environmental exposure to toxic chemicals has been strongly associated with neurotoxicity, particularly through

mechanisms involving oxidative stress and lipid peroxidation in brain tissues. Among these environmental

pollutants, mercury chloride (HgCl₂) is a well-known neurotoxicant that affects the central nervous system and

has been implicated in the development of several neurological disorders [7], including Parkinson’s disease,

Alzheimer’s disease and Huntington’s disease. Mercury, a heavy metal of global concern is introduced into the

ecosystem through both natural and anthropogenic activities, leading to its persistence and bioaccumulation in

humans and animals. Due to its unique physicochemical properties, mercury deeply affects human health and

has been linked to cognitive dysfunction and other neurological disorders related to neuroinflammation and

Parkinson’s disease and Huntington’s disease.

Increasing research indicates that mercury-related neurotoxicity may compromise the functional integrity of the

basal ganglia. Given this region's critical involvement in both motor and cognitive functions, it is vital to explore

how mercury exposure affects its neuronal health, particularly in relation to Alzheimer’s disease-like symptoms.

The pathogenesis of mercury-induced neurotoxicity is primarily associated with oxidative stress, leading to

neuronal damage, neurotransmitter imbalances and cognitive deficits characteristic of Alzheimer’s disease.

Oxidative stress disrupts the delicate balance of antioxidants, such as superoxide dismutase (SOD) and elevates

lipid peroxidation markers, including malondialdehyde (MDA). It also impairs enzymes critical for neural

function, including acetylcholinesterase (AChE). Additionally, mercury accumulation contributes to

pathological changes such as neuronal pyknosis and amyloid plaque deposition, which are hallmarks of

including neurodegenerative disorders like Alzheimer’s disease and other neurological impairments ([20],[27]).

These plants are rich in bioactive phytochemicals—such as flavonoids, alkaloids, terpenoids and polyphenols—

that not only neutralize harmful free radicals but also modulate key biological pathways involved in

inflammation, immune response, and cellular repair.

Their multifaceted healing potential stems from a synergistic blend of pharmacological actions. Anti-

inflammatory compounds help reduce neuroinflammation, a hallmark of many brain disorders. Antioxidants

protect neurons from oxidative stress, which is implicated in the progression of Alzheimer’s and Parkinson’s

diseases. Immunomodulatory agents enhance the body’s defense mechanisms, while anticancer and

antimicrobial constituents broaden their application to oncology and infectious disease management [19].Beyond

their biochemical effects, medicinal plants offer a holistic approach to healing, often aligning with traditional

such as aloe-emodin, aloin, aloesin, emodin, and acemannan, linked to pharmacological effects like anticancer,

antioxidant, antidiabetic and antihyperlipidemic actions ([8],[14]).

This study investigates whether the ethanolic leaf extract of Aloe barbadensis (Aloe vera) can counteract the

neurodegenerative effects of mercury chloride exposure, which is known to induce Alzheimer-like symptoms in

the basal ganglia of albino Wistar rats. Mercury chloride is a potent neurotoxin that disrupts neuronal function

primarily through oxidative stress, leading to behavioral impairments, biochemical imbalances, and structural

brain damage that resemble the pathology of Alzheimer’s disease.

To address this, the study evaluates the extent to which Aloe barbadensis extract can restore normal brain

function by targeting key markers of neurotoxicity. These include behavioral parameters such as anxiety and

memory performance, assessed through open field and novel object recognition tests. On a biochemical level,

mercury-induced neurodegeneration and Alzheimer-like conditions.

The study was conducted in the animal house unit, Department of Human Anatomy, Faculty of Basic medical

Sciences, Chukwuemeka Odumegwu University, Uli campus. With 35 adult male wistar rats weighing 130 –

150g.The rats were kept in standard cages at room temperature of 27±2°C and was maintained on 12-hours light

and dark cycles to maintain the normal circadian rhythm fed with standardized pellet grower’s feed and distilled

water ad libitum. The rats were acclimatized for two weeks for physiological adaptation to the animal house

before administering mercury chloride and ethanol extracts of Aloe barbadensis miller.

Aloe barbadensis miller (Aloe-vera) was obtained from a local farm in Nnewi North and was washed to remove

dirt. The dried aloe-vera was milled into a coarse powdered form using a local grinder. About 250 g each of the

This was obtained from the ethical committee, faculty of basic medical sciences Chukwuemeka Odumegwu

Ojukwu University, Uli campus in compliance with the relevant laws and institution’s guidelines.

All authors hereby declare that "Principles of laboratory animal care" (NIH publication No. 85-23, revised 1985)

were followed, as well as specific national laws where applicable. All experiments have been examined and

approved by the appropriate ethics committee.

All animals were housed under same environmental conditions throughout the study. Thirty-five rats were

randomly assigned into five groups (n = 7). Group A served as the negative control and received feed and water

only. Group B, received 5 mg/kg of mercury chloride for 3 weeks. Group C was administered 500 mg/kg of Aloe

barbadensis extract for 3 weeks. Group D and E received 5 mg/kg of mercury chloride for 3 weeks, followed by

processed for routine Hematoxylin and eosin and silver Beilschowsky staining.

Data were analyzed using GraphPad Prism version 9.5.1. One-way ANOVA followed by Fisher’s Least

Significant Difference (LSD) post hoc test was used to analyze brain levels of MDA, SOD, glutamate,

acetylcholinesterase activity, anxiety index, and recognition memory. Histological findings, including amyloid

plaque deposition, were also evaluated descriptively. Results were expressed as mean ± standard error of the

mean (SEM), and differences were considered statistically significant at p ≤ 0.05.

Figure 1: Effect of ethanolic extract of Aloe barbadensis Miller on anxiety index following mercury chloride

exposed rats.

exposed rats.

showing numerous large neurons (N) and the glial cells. Stained with H & E (x400). Figure 9

Figure 10: Group D (H&E staining)

of the neurofibrillary tangle and mild positive staining of the senile plaques (arrow) (Bielschowsky X400). Figure

13

Figure 14: Group C (Silver Beilschowsky Stain).

Group C (500 mg/kg of Ethanolic extract of aloe barbadensis): A section of brain (Basal ganglion) section of

albino rat shows negative staining of the neurofibrillary tangle senile plaques (Bielschowsky X400). Figure 14

Figure 15: Group D (Silver Beilschowsky Stain).

Group D (5mg/kg of HgCl2 for 3-weeks + 250 mg/kg of Ethanolic extract of aloe barbadensis): A section of

brain (Basal ganglion) section of albino rat shows negative staining of the neurofibrillary and Senile plaques

The primary objective of this research was to assess the ameliorative effects of ethanolic leaf extract from Aloe

barbadensis (Aloe vera) against the neurotoxic impact of mercury chloride, which is known to provoke

Alzheimer-like symptoms in the basal ganglia of albino Wistar rats. Mercury chloride, identified as a hazardous

environmental pollutant, interferes with brain function by promoting oxidative stress and cellular damage

([17],[18]). Its neurotoxicity manifests through behavioral disturbances, biochemical disruptions, and structural

degeneration that resemble Alzheimer’s disease pathology[18]. Given the therapeutic promise of plant-based

compounds, Aloe barbadensis, rich in antioxidants like aloin, aloe-emodin, and ace Mannan, was selected for its

potential to counteract these effects ([20],[6]). This study explored its influence on anxiety and memory behavior,

oxidative stress markers, neurotransmitter levels, and histological changes in brain tissue, aiming to establish its

role as a natural intervention for mercury-induced neurodegeneration.

anxiety index compared to both the untreated control group and those treated with Aloe barbadensis. This

behavioral alteration aligns with established literature indicating that mercury disrupts neurotransmitter systems

and induces oxidative stress, particularly in brain regions responsible for emotional regulation ([17],[18]).

Interestingly, Group C, which received only Aloe barbadensis extract without mercury exposure, demonstrated

a significant reduction in anxiety index relative to the control group. This suggests that the extract may possess

intrinsic anxiolytic properties, potentially mediated by its rich phytochemical composition—including

polysaccharides, flavonoids, and anthraquinones—which are known to modulate oxidative pathways and

neuroinflammation ([6]; [16]). The anxiolytic-like effects observed in the Aloe-treated groups (D and E) further

support the hypothesis that Aloe barbadensis can counteract mercury-induced emotional disturbances.

In the novel object recognition test, which assesses recognition memory, rats in Groups C, D, and E exhibited